# Proxy\_pass with / in the end causes SYN packets? **URL:** \ **Category:** NGINX\ **Tags:** openresty, packets, reverse-proxy\ **Created:** [February 14, 2025, 5:18am UTC](https://community.nginx.org/t/proxy-pass-with-in-the-end-causes-syn-packets/421 "2025-02-14T05:18:47Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![yasoo7964](https://drob5swvtjqxg.cloudfront.net/user_avatar/community.nginx.org/yasoo7964/32/307_2.png) [@yasoo7964](https://community.nginx.org/u/yasoo7964)\ **Post date:** [February 14, 2025, 5:18am UTC](https://community.nginx.org/t/proxy-pass-with-in-the-end-causes-syn-packets/421/1 "2025-02-14T05:18:47Z")
Hi, now i’m making Reverse Proxy by using Nginx1.25.3(openresty1.25.3.1), i have one backend backend1:192.168.62.60 that has no content\_path so i set up nginx.conf like below. and i wanna have other backends so give it a location keyword in the request uri as “/backend1”, and call proxy\_pass with / in the end(remove “/backend1” from request\_uri). then when i was looking into the packets between Nginx and backend1 with WireShark, i’ve noticed that SYN packets are increased than when i connected directly from browser to backend1. heard many suggestions that Keep-Alive may be involved, so i tried the parameters related to it, but there was no change. In the WireShark view, Connection parameter in the sent HTTP request, are always set as “Keep-Alive”, but Nginx always sends FIN,ACK packet at the end of each tcp sequence started by one HTTP request from it’s side. Any suggestion, please. Thanks in advance. Best regards. Yasoo7964 ---- nginx.conf --------- ```auto http { upstream backend1_server { server 192.168.62.60; keepalive 32; } server { listen 80; listen 443 ssl; ssl_certificate /etc/ssl/rootCA/gw.com/certs/gw.com.crt.pem; ssl_password_file /etc/ssl/rootCA/gw.com/pwf; ssl_certificate_key /etc/ssl/rootCA/gw.com/private/privkey.pem; server_name 192.168.52.111; proxy_http_version 1.1; proxy_set_header Upgrade $http_upgrade; proxy_set_header Connection "Keep-Alive"; proxy_set_header Host $host; proxy_set_header X-Real-IP $remote_addr; proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for; proxy_set_header X-Forwarded-Proto $scheme; keepalive_timeout 60s; keepalive_requests 100; proxy_connect_timeout 5s; proxy_read_timeout 60s; proxy_max_temp_file_size 0; sendfile off; etag off; if_modified_since off; location /backend1/ { proxy_pass http://backend1_server/; proxy_redirect / /backend1/; header_filter_by_lua_block { rewrite_resp.header_filter() } body_filter_by_lua_block { rewrite_resp.body_filter(ngx.var.scheme, ngx.var.server_name, "backend1") } } } } ``` ---
**Author:** ![s.miller](https://drob5swvtjqxg.cloudfront.net/user_avatar/community.nginx.org/s.miller/32/39_2.png) [@s.miller](https://community.nginx.org/u/s.miller)\ **Post date:** [February 14, 2025, 5:21am UTC](https://community.nginx.org/t/proxy-pass-with-in-the-end-causes-syn-packets/421/2 "2025-02-14T05:21:08Z")
Moved this to the Troubleshooting category. ---
**Author:** ![yasoo7964](https://drob5swvtjqxg.cloudfront.net/user_avatar/community.nginx.org/yasoo7964/32/307_2.png) [@yasoo7964](https://community.nginx.org/u/yasoo7964)\ **Post date:** [February 14, 2025, 8:50am UTC](https://community.nginx.org/t/proxy-pass-with-in-the-end-causes-syn-packets/421/3 "2025-02-14T08:50:01Z")
Note: I asked this question because GPT said, ``Adding / to the end of proxy\_pass, in other words, rewriting the HTTP request, may increase the number of SYN packets.‘’ ---
**Author:** ![yasoo7964](https://drob5swvtjqxg.cloudfront.net/user_avatar/community.nginx.org/yasoo7964/32/307_2.png) [@yasoo7964](https://community.nginx.org/u/yasoo7964)\ **Post date:** [February 18, 2025, 6:07am UTC](https://community.nginx.org/t/proxy-pass-with-in-the-end-causes-syn-packets/421/4 "2025-02-18T06:07:29Z")
with further investigation, i found that backend1 does not support HTTP/1.1, so even though Nginx sends HTTP/1.1 request, backend1 always reply “HTTP/1.0 200 OK”. In HTTP/1.0, it is correct behavior to create a new socket for each request. sorry for asking an irrelevant question. On the other hand, when i directly connect to backend1 with Edge, Edge does not send FIN,ACK even when it receives “HTTP/1.0 200 OK”, and reuses the socket. so i look into the “HTTP/1.0 200 OK”, it attached “Connection:Keep-Alive” option. and i’ve heard that even in HTTP/1.0, it can reuse the socket with the option. Does Nginx not support it? ---
**Author:** ![Damian\_Curry](https://avatars.discourse-cdn.com/v4/letter/d/94ad74/32.png) [@Damian\_Curry](https://community.nginx.org/u/Damian_Curry)\ **Post date:** [February 18, 2025, 7:52pm UTC](https://community.nginx.org/t/proxy-pass-with-in-the-end-causes-syn-packets/421/5 "2025-02-18T19:52:19Z")
If you upstream service does not support HTTP/1.1, you should remove the `proxy_http_version 1.1;` from your configuration, as this is setting communication for the upstream to use version 1.1. Without this directive, nginx will default to using HTTP/1 when proxying traffic to the upstream. ---
**Author:** ![yasoo7964](https://drob5swvtjqxg.cloudfront.net/user_avatar/community.nginx.org/yasoo7964/32/307_2.png) [@yasoo7964](https://community.nginx.org/u/yasoo7964)\ **Post date:** [February 19, 2025, 12:38am UTC](https://community.nginx.org/t/proxy-pass-with-in-the-end-causes-syn-packets/421/6 "2025-02-19T00:38:29Z")
Thank you Damian, i’ve tried it so Nginx sends GET xxxx HTTP/1.0 with Connection:Keep-Alive, and then upstream replies as HTTP/1.0 200 OK with Connection:Keep-Alive, but Nginx replies with FIN,ACK to it. 627 12.026094427 192.168.62.111 192.168.62.60 TCP 74 0 51946 → 80 [SYN] Seq=0 Win=64240 Len=0 MSS=1460 SACK\_PERM=1 TSval=1540337777 TSecr=0 WS=128 628 12.027588129 192.168.62.60 192.168.62.111 TCP 62 0 80 → 51946 [SYN, ACK] Seq=0 Ack=1 Win=14600 Len=0 MSS=1460 SACK\_PERM=1 629 12.027961381 192.168.62.111 192.168.62.60 TCP 54 1 51946 → 80 [ACK] Seq=1 Ack=1 Win=64240 Len=0 630 12.029281992 192.168.62.111 192.168.62.60 HTTP 792 1 GET /date.htm HTTP/1.0 ``` GET /date.htm HTTP/1.0\r\n Connection: Keep-Alive\r\n ``` 631 12.030395246 192.168.62.60 192.168.62.111 TCP 60 1 80 → 51946 [ACK] Seq=1 Ack=739 Win=15498 Len=0 632 12.030633835 192.168.62.60 192.168.62.111 TCP 238 1 80 → 51946 [PSH, ACK] Seq=1 Ack=739 Win=15498 Len=184 [TCP segment of a reassembled PDU] 633 12.030667413 192.168.62.111 192.168.62.60 TCP 54 739 51946 → 80 [ACK] Seq=739 Ack=185 Win=64056 Len=0 634 12.030814113 192.168.62.60 192.168.62.111 HTTP 1292 185 HTTP/1.0 200 OK (text/html) ``` HTTP/1.0 200 OK\r\n Connection: Keep-Alive\r\n ``` 635 12.030824244 192.168.62.111 192.168.62.60 TCP 54 739 51946 → 80 [ACK] Seq=739 Ack=1423 Win=64056 Len=0 636 12.030895231 192.168.62.111 192.168.62.60 TCP 54 739 51946 → 80 [FIN, ACK] Seq=739 Ack=1423 Win=64056 Len=0 637 12.031795309 192.168.62.60 192.168.62.111 TCP 60 1423 80 → 51946 [FIN, ACK] Seq=1423 Ack=740 Win=15498 Len=0 638 12.031829625 192.168.62.111 192.168.62.60 TCP 54 740 51946 → 80 [ACK] Seq=740 Ack=1424 Win=64056 Len=0 ---
**Author:** ![alessandro](https://drob5swvtjqxg.cloudfront.net/user_avatar/community.nginx.org/alessandro/32/4836_2.png) [@alessandro](https://community.nginx.org/u/alessandro)\ **Post date:** [June 23, 2025, 1:16pm UTC](https://community.nginx.org/t/proxy-pass-with-in-the-end-causes-syn-packets/421/7 "2025-06-23T13:16:08Z")
Hey @yasoo7964. Where you able to figure this out in the end? ---
**Author:** ![system](https://drob5swvtjqxg.cloudfront.net/user_avatar/community.nginx.org/system/32/19_2.png) [@system](https://community.nginx.org/u/system)\ **Post date:** [July 23, 2025, 1:16pm UTC](https://community.nginx.org/t/proxy-pass-with-in-the-end-causes-syn-packets/421/8 "2025-07-23T13:16:15Z")
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